Interference reducing means for radio receiving apparatus



R. H. RANGER Juixe 3, 1930.

INTERFERENCE REDUCING MEANS FOR RADIO RECEIVING APPARATUS Filed 056. 1s .;-1e22 2 Sheets-Sheet 1 z m M u a June 1930. R. H. RANGER 1,761,049

INTERFERENCE REDUCING MEANS FOR RADIO RECEIVING APPARATUS Filed D60. 18. 1922 2 SheetsR-Shet 2 anoentoz -H- RANGER @31 has y a Patented June 3, 1930 UNITED STATES nransin PATENT OFFICE RICHARD HOWLAND' RANGER, OF NEW YORK, N. Y., ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE INTERFERENCE REDUCING MEANS FOR RADIO RECEIVING API'ARATUS Application filed December 18, 1922. Serial No. 607,477.

This invention relates to means for reducing interference in the reception of radio signals, and more specifically, to improved means for receiving signals from two receiving stations on a common indicating means.

It is an object of this invention to provide improved means for receiving signals from a desired station and eliminating signals from other stations, especially those transmitting on substantially the same wave length. It is a further object of this invention to provide such means which shall be simple and inexpensive to build and install, and reliable and efiective in operation. Still other objects will be seen from the specification.

My invention is illustrated by way of example in the accompanying drawings in which Figure 1 shows diagramatically the arrangement of transmitting and receiving stations.

Figure 2 illustrates the preferred embodiment of my invention.

Figure 3 is a possible modification thereof.

Figure 4 is still another modification, and

Figure 5 is a diagrammatic comparison of the results obtained from old apparatus and those obtained from my invention.

Referring to Fig. 1, it is well known in the art that a wave transmitted from station A, for instance, will be received at stations B and B at difierent times. To be sure this difference in time of reception is very small but if the signals are let to acommon indicating means such as G this difference in time under certain conditions is suflicient to cause considerable difference in phase between signals received at B and those received at B. Means for controlling the phase of the signals with respect to each other are known and may take the form of phase rotators or phase shifting coils. By adjusting these means, it is possible to bring signals into phase at the indicating apparatus. As the signals are being brought into phase they combine according to the law of cosines as shown by the dotted line curve in Fig. 5, whose ordinates represent intensity of signals in the indicating means andwhose abscissae represent the portional to cos (0 --6 where 6 and 0 difierence in phase between the signals. While this provides for a certain amount of geographical selectivity between transmitting stations on the same wave length, it still leaves much to be desired. A curve such as shown in full lines in Figure 5 is much more desirable, since this gives maximum response for signals substantially in phase and minimum response for signals dephased by a substantial amount.

In accordance with this invention I introduce such means in the circuit that the intensity of signals in the circuit is proportional to the cosine of the angle of phase difference between the signals, and in addition, further means to control the s gnals again in accordance with the cosine of the angle of phase difference of signals, giving in the output circuit a signal whose intensity is prorepresent the phase angles of the signal currents as will hereinafter be described.

My invention will best be understood by reference to the specification and the attached drawings, but its scope will be pointed out in I the claims.

Referring to Figure 2, B and B are two receiving stations whose aerials differ in physical or electrical characteristics with reference to the desired signal, as described in my copending application, Serial No. 607 ,47 8, filed December 18, 1922, and are provided with the usual tuning means, such as variable inductances 2 and 2 and variable capacities 3 and 3. The oscillations received upon the 85 antennae are impressed on the grid circuits of the vacuum tub-e amplifiers 4 and 4' in the usual manner. Connected in the plate circuit of these tubes I provide a choke coil 5 having a core 6 of magnetic material. This choke coil will be arranged in such a way that the normal alternating plate current circulating in the winding 5 will set up a magnetic field in opposition to that of the current circulating in the winding 5". This may be achieved 95 by winding the two coils in the same direct on and connecting the two windings for current flow in the reversed direction in each coil and the choking action thereby produced is a function of the cosine of the phase angle 1001 difference which will be multiplied by the quantity cos (0 6 which is the angle of phase difference already existing in the two separate receiving circuits and appearing in the windings 7 and 8 of the coupling coils 7 and 8 to be hereinafter described, or if desired the coils may be connected so as to have the current flowing in the same direction but the windings arranged in opposite directions whereby an opposing electromagnetic field will be produced. In the plate circuit 4. I provide also a coupling coil 7 having primary 7 and secondary 7 and in a similar manner I provide coupling coil 8 in plate circuit of tube 4'. The secondaries 7 and 8 are connected in series in such a manner that the currents add vectorially. I provide also in circuit with the secondaries 7 and 8 of coupling coils 7 and 8 a suitable detector 9, which may be a vacuum tube, and indicating apparatus such as telephone receivers 10.

The operation of my invention is as follows. Let us assume that station A is transmitting and that the operator at C desires to listen. Receivers B and B are tuned in the usual manner, that is, each is tuned to the wave length of transmitter A. It will be apparent that a difi'erence in phase will existbetween the currents flowing in the plate circuits of tubes 4 and 4. Let us neglect for the moment the effect of the alternating current fiow in plate circuit of tube 4. It will be evident that coil 5 will present a very high impedance to the flow of alternating current in the plate circuit, more especially since these alternating currents are fluctuating at radio frequency and coil5has a magneticcore, and, as above stated, acts as a choke coil to offer high impedance to the radio frequency, currents under conditions to be hereinafter described. This impedance is chosen so as to substantially reduce fluctuations of the plate current according to the phase angle of the two received signals upon the receiving systems B and B. Assume now, that signals arriving at B have a phase difference of 180 from those in B. Since the magnetic fields produced by 5 and 5 are in opposition where the signals are in' phase, these fields will now be in phase and will add together thus increasing the impedance of coils 5 and 5 and effectively increasing the impedance of these coils. On the other hand if signals from B are brought into phase with those from B, it is apparent that the magnetic field of the coil 5 will neutralize that of coil 5 giving a resultant impedance of very much lower value than that obtained when the currents are out of phase or where the signals are in-phase there is maximum current and minimum reduction of the alternating current component due to the choking action of the choke 5 and where the signals are 180 out of phase there is minimum current and maximum reduction due to the choking action. This is because the choking action of 5 is proportional to the cosine function of the phase angle difference of the signals received upon the two receiving systems. Under these circumstances alternating current of a normal value dependent upon the signals and relative phase relationship will flow in the plate circuit of each tube and a corresponding current will be induced in the secondary windings 7 b and 8 of coupling coil 7 These induced currents add vectorially and when combined actuate the common detector 9 and the indicating apparatus 10. Thus itwill be apparent that when the signals at C are in phase the maximum response will be obtained from the indicating apparatus 10, but if the signals are out of phase by any considerable amount the magnetic fields produced in 6 will not neutralize each other but may even reinforce each other, and in such case the voltages impressed on the detector 9 will be out of phase to that degree, thus giving a detector voltage=K cos (0 -6 which will effectively prevent operation of the indicating means, Where K is a function of the properties of the entire system, for example, the choke 5, the phase rotator, the tubes, and, in fact, the general efliciency of all the system. It is apparent that to provide means for geographically tuning to bring in any desired station it is necessary to provide phase shifting coils or phase rotators, as are conventionally indicated in the line connecting with antenna system B, to control the phase of the signals at C so that no matter what the phase of the signals at B and B may be, the signals may be brought substantially into phase at C.

Referring to Figure 3, if desired I may place the choke coil 5 in circuits which are coupled to the plate circuit instead of placing it in the plate circuit itself as shown in F igure 2. As shown in Figure 3 I provide in the plate circuit of tubes 1 and 4 coupling coils 10 and 11. The secondaries 10 and 11 are connected respectively to one side of condensers 14 and 14: and to one winding of transformer 5. The circuits 14, 10 5 and 14:, 11 5 are completed through coupling coils 15 and 13 respectively. The secondaries of coupling coils 13 and 15 may be connected in series as in Figure 2 with a common detecting means or as shown in Figure 3 they may be connected to individual amplifiers and the tubes of these amplifiers combined to actuate the indicating means. It is apparent that the natural frequency of the circuits may be adjusted by means of the variable condensers 14 and 14. The operation of this modification is essentially the same as that of the embodiment shown in Figure 2; that is, when the signals at C received at B and B are in phase the resulting magnetic field linking the choke coil 5 is very small and the impedance of these circuits is correspondingly small whereby the currents will be passed on to amplifiers 17 and 18 and thence to the indicating instrument. However, for any considerable difference in phase between these currents only a very small current will pass through the amplifiers giving a minimum response in the indicating apparatus.

Referring to Figure 4 still another modification may be employed. In this case I utilize a frequency trap without a magnetic core. In the plate circuit of tube 4 I place an inductance 20 closely coupled to inductance 21 and in a similar manner in the plate circuit of tube 4 I place inductance 22 coupled to inductance 23. The circuit of 21 and 23 is completed as shown by means of variable condenser 24. The operation of this modification is essentially the same as that shown in Figure 3. Assuming that signals impressed upon tubes 4 and 4 are in phase,the alternating current may be assumed to flow from coil 20 at any instant as indicated by the arrow. If the trap is tuned by means of condenser 24 the corresponding current will flow in series through condenser 24 and coils 21 and 23 in such a manner as to neutralize the magnetic field due to the current in coil 20 and it will be seen that this current will also neutralize the magnetic field produced by plate current of tube 4. It is, therefore, evident that when these currents are in phase the resultant impedance of the external part of the plate circuit will be very low and the usual current will flow. The alternating current flowing in the two plate circuits 4 and 4 may be combined as shown by means of the coupling coils 7 and 8 in such a way as to add under the desired conditions or they may be separately amplified and then combined by vectorially adding together in the detector circuit 9.

The currents indicated on the drawings by arrows are intended to represent the instantaneous values of the alternating currents, and the sole purpose of the direct current sources shown by the various batteries is to cause the various tubes to function as linear amplifiers. Further, it should be understood that the process herein described for combining signals is not a saturation process, since the direct current supplied as anode potential does not saturate the iron core choke coil members.

While I have shown and described my invention in its preferred embodiment it will be apparent that many modifications and changes may be made without departing from the spirit of my invention.

Having described my invention I declare that what I claim is 1. In radio signalling apparatus the combination of a plurality of aerials, means for indicating the resultant of signals received upon each aerial and means offering a low impedance to the flow of current controlling said indicating means only when said slgnals have a predetermined phase relation.

2. In radio signalling apparatus the combination of a plurality of receiving systems having a common indicating means and means for coupling said receiving systems for presenting a high impedance to received oscillations whose phase difference differs from predetermined value.

3. In radio signalling apparatus, the combination of two aerials, means for indicating the resultant of signals received upon both aerials and means for causing the response of said indicating means to be proportional to a power greater than unity of a function of the angle of phase difference between said signals.

4. In radio signalling apparatus, the combination of two aerials, means for indicating the resultant of signals received on both said aerials and means for causing the response of said indicating means to be proportional to the square of a function of the angle of phase difierence between said signals.

5. In radio signalling apparatus, the combination of a plurality of aerials, a normally high impedance coupling coil connecting said aerials in such a manner that the magnetic field of said coupling coil will be a minimum for a predetermined phase difference between signals received on said aerials, and indicating apparatus arranged to respond to the resultant of said signals.

6. In radio signalling apparatus, the combination of a plurality of receiving systems, a common indicating means, and normally high impedance means connecting said systems and said indicating means, said means substantially reducing fluctuations of current therein except under predetermined' nditions. ikln radio signalling systems, the comination of a plurality of aerials, each tuned to the same desired signal frequency amplifiers associated with each aerial, a high impedance coil having a Winding connected in the output circuit of'each amplifier, and detecting and indicating apparatus arranged to indicate the resultant of signals received on each aerial.

8. In radio signalling apparatus, the combination of a plurality of aerials, each tuned to the same desired signal frequency, amplifiers associated with each aerial, a closed circuit normally of high impedance coupled to the output circuit of each amplifier, said circuits being coupled together, and detect ing and indicating means associated with said circuits.

9. The combination claimed in claim 7 with means for adjusting the natural frequency of said high impedance circuits.

10. In radio signalling apparatus the combination of a plurality of aerials, each tuned to the same desired signal frequency amplifying means connected to each aerial, a he 5 quency trap, said trap bein coupled to the output circuit of each ampli er, and common detecting and indicating means associated With the output circuits of said amplifiers.

RICHARD HOWLAND RANGER. 

